The brief argues that the preamble does not restrict the operative clause. "interstate" does restrict/modify "commerce"
Although Congress is also given the power to regulate foreign commerce and commerce with the Indian nations. Congress has only those powers specifically delegated to it. They were only delegated the power to regulate those three types of commerce. Certainly not "intrastate commerce" nor "anything which affects" the commerce they have the power to regulate, since that would be pretty everything.
The two situation are not even comparable.
I'm simply saying you wouldn't ever let the U.S. Supeme Court get away with such a rereading of the text. And you know you wouldn't.